1. Field of Invention
The present invention relates to lasers and more particularly to systems for actively controlling the surface of a laser mirror.
2. Description of the Prior Art
In systems requiring the transmission of laser radiation, the intensity of the beam at the point of ultimate utility is often very important. The success or failure of some applications may be determined completely by whether the intensity of the laser radiation reaching the target complies with at least some minimum criteria. Fundamentally, the phase of laser beam is subject to distortion by events occurring inside the generating mechanism which may be an oscillator or amplifier or a combination thereof or events that occur during propagation of the beam from the point of origin to the target.
One technique for improving the quality of the energy at a target is with a closed loop system having an element of feedback from the target site. Such a system is described in U.S. Pat. No. 3,731,103 entitled Adaptive Arrays issued May 1, 1973 to T. R. O'Meara. In this system a plurality of laser sources is directed at a target, each being phase modulated at a different frequency. Signals reflected from the target are collected and processed so that each laser source is preconditioned in order to yield the phase relationship desired at the target. The system involves multiple transmitting surfaces, a receiving surface and suitable equipment to condition the radiation leaving each transmission surface in accordance with the information being received at the collecting surface.
Another system involving adaptive optics was discussed at the Woods Hole Summer Seminar held in August, 1967 and published by the National Academy of Sciences in AD680797 as the Perkin-Elmer Program in Active Figure Control by D. A. Markle. The article describes a closed loop, servocontrolled system which was developed for use with a large telescope. A major problem being overcome with this system is the imprecision of manufacture inherent in a large surface collector. Basically, the overall telescope surface is so large and the variation from an ideal surface which is allowable in order to maintain the sensitivity desired is so small that significant changes must be made to the surface after manufacture and at various times thereafter. The main elements of the system comprise an optical sensor which looks at the surface of the telescope, an error computer, and some control logic to manipulate actuators which correct for tilt and axial misalignment of the telescope surface.